1. Field of the Invention
The present invention relates to a mask, a manufacturing method for a mask, and a manufacturing method for a semiconductor device.
2. Description of the Related Art
The inventors have already proposed a focus monitor mask used to measure the magnitude of defocus in an exposure apparatus including the sign of the defocus (refer to Jpn. Pat. Appln. Nos. 11-274701 and 11-375472, which correspond to U.S. Pat. No. 6,440,616). FIG. 20 illustrates an example of this focus monitor mask. This figure schematically shows a planar configuration of a mask pattern formed area.
The mask pattern formed area includes a reference mark area 10 and a phase shift mark area 20. The reference mark area 10 has a surrounding portion (surrounding area) 11 including an opaque portion or a halftone portion and five opening portions (opening areas) 12 surrounded by the surrounding portion 11. The phase shift mark area 20 has a surrounding portion 21 including a halftone portion and five opening portions 22 surrounded by the surrounding portion 21. The opening portions 12 and 22 are used as focus monitor marks and have the same diamond-like (rhomboid-like) planar shape. A phase difference between the opening portions 22 and the surrounding portion 21 is set to be 90°. Accordingly, there is a phase difference of 90° between exposure light passing through the opening portions 22 and exposure light passing through the surrounding portion 21.
The use of a mask configured as described above enables focus monitoring. This focus monitoring utilizes misalignment that may occur between the best focus point for the pattern (reference mark) of the opening portions 12 and the best focus point for the pattern (phase shift mark) of the opening portions 22. A monotonous decrease or increase relative to defocus is observed in a size difference between a long side of the reference mark and a long side of the phase shift mark which difference may occur after exposure or development. Thus, by determining the relationship between defocus and this size difference in the form of a calibration curve and subsequently measuring a size difference on a wafer after exposure and development, the magnitude of defocus can be monitored including its direction.
FIG. 22 shows the relationship (calibration curve) between a size difference (L-L′) and defocus where L denotes the size of a long side of a reference mark on a wafer and L′ denotes the size of a long side of a phase shift mark on the wafer. A line a indicates the size L of the reference mark. A line b indicates the size L′ of the phase shift mark. A line c indicates the size difference (L-L′). The size difference c increases monotonously relative to defocus. Accordingly, this calibration curve can be used to determine the magnitude of defocus including its sign. In this connection, varying the magnitude of exposure by ±10% does not substantially change the calibration curve. Therefore, even with a slight variation in the magnitude of exposure, the defocus can be accurately detected.
Now, description will be given of a manufacturing method for a conventional mask having a pattern such as the one shown in FIG. 20. FIGS. 21A to 21H schematically show cross sections taken along line A-A′ in FIG. 20.
First, as shown in FIG. 21A, a quartz substrate is provided as a transparent substrate 101. An MoSiOx film is formed on the transparent substrate 101 as a halftone phase shift film 102. Subsequently, a Cr film is formed on the halftone phase shift film 102 as an opaque film 103. Furthermore, a chemically amplified positive type resist 104 is applied to the opaque film 103. The halftone phase shift film 102 sets a phase difference of 180° between exposure light passing through the halftone phase shift film 102 and exposure light passing through the opening portion 12.
Then, as shown in FIG. 21B, focus monitor marks are written in the resist film 104 in a reference mark area and a phase shift mark area. At this time, device pattern is also written in a device pattern forming area (not shown). Subsequently, the substrate is baked and then development is carried out to form a resist pattern 104.
Then, as shown in FIG. 21C, the opaque film 103 and the halftone phase shift film 102 are sequentially etched using the resist pattern 104 as a mask. This etching forms a focus monitor mark pattern corresponding to the planar shape of the opening portions 12 and 22 as well as a device pattern (not shown). Subsequently, the resist film 104 is removed and the substrate is cleaned.
Then, as shown in FIG. 21D, an i-ray photo resist 151 is applied. Subsequently, to mask the area except for the opening portions of the phase shift mark, a writing operation is performed using a laser writing apparatus. Furthermore, a developer is used to carry out development to obtain a resist pattern 151.
Then, as shown in FIG. 21E, the transparent substrate 101 is etched using the resist pattern 151 and the opaque film 103 as a mask. This allows the transparent substrate 101 to be etched only in the opening portions of the phase shift mark to form holes 152.
Then, as shown in FIG. 21F, the resist 151 is removed and the substrate is cleaned.
Then, as shown in FIG. 21G, an i-ray photo resist 153 is applied. Subsequently, to mask the opening portions in the reference mark area 10, Cr opaque frame portions, and other Cr pattern portions, the laser writing apparatus is used to write in the resist film 153. Furthermore, a developer is used to carry out development to obtain a resist pattern 153.
Then, as shown in FIG. 21H, the resist pattern 153 is used as a mask to wet-etch the opaque film 103. Subsequently, the resist film 153 is removed and the substrate is cleaned.
A mask configured as shown in FIGS. 20 and 21H is obtained as described above. Since the transparent substrate 101 is etched to form the holes 152, it is possible to give a phase difference of −90° to exposure light passing through the opening portions in the phase shift mark area 20 relative to exposure light passing through the opening portions in the reference mark area 10.
However, with the above conventional manufacturing method, extra lithography and etching steps such as those shown in FIGS. 21D to 21F are required to form the holes 152 used to create a phase difference of 90°. This sharply increases the time required for a manufacturing process, thus affecting manufacturing costs and TAT.
Thus, the conventional focus monitor mask requires extra lithography steps to obtain a phase difference of 90°. This increases the time required for the manufacturing process, thus increasing manufacturing costs.